Influence of the biaxial loading regimes on fatigue life of 2024 aluminum alloy and 40CrMnMo steel

The work studies the fatigue life of metallic materials under various schemes of multiaxial non-proportional loading which lead to the occurrence of a complex stress-strain state. We present the results of the experimental study of the fatigue life of 40CrMnMo structural alloyed steel and 2024 aluminum alloy under biaxial cyclic loading. Cyclic tests were carried out on the Instron ElectroPuls E10000 biaxial electrodynamic test system under joint tension-compression and torsion of solid cylindrical corset-type samples. The methodological issues of conducting cyclic tests with a mixed modes loading are considered and the corresponding new experimental results are obtained. The experimental data are presented in the form of points on the graphs and corresponding approximating lines which reflect the dependence of the number of cycles to failure on the relative values of the constant components of the tangential and normal stresses. In all the tests, the specified values of the additional parts of the stress components did not exceed the values of the corresponding conditional yield strengths, which were previously determined in the quasistatic tensile and torsion tests for each material. Based on the test results, the influence of the constant component of tangential stresses on the fatigue life of the materials under cyclic tension-compression was evaluated, and the effect of the constant component of normal stresses on the fatigue life under cyclic torsion was considered. It is shown that because of the constant stress components, both under cyclic tension-compression and cyclic torsion, there is a decrease in the number of cycles before the specimens break. The obtained data demonstrate the necessity to estimate the allowable limits of the constant parts of the stress components, which will not lead to a significant reduction in the fatigue life of structures operating under cyclic loading conditions.